This invention relates to a soldering process and apparatus and in particular to an inert atmosphere spot soldering process and apparatus.
In my prior U.S. Pat. No. 5,439,158 I disclosed a soldering system having a controlled atmosphere bathing the solder pot and all liquid solder surfaces. In my prior U.S. Pat. No. 5,335,843 I disclosed a spot soldering apparatus which controlled the solder level and immersion of the leads by the meniscus formed by solder in pockets in which the terminals were then immersed.
In some situations the terminals to be soldered may be scattered around a printed circuit board and require a multiplicity of pockets properly located to solder a number of terminals substantially simultaneously. At the same time it is desirable that the pockets, terminals and solder surfaces be protected by an inert atmosphere as efficiently as possible.
In soldering terminals which are close together bridging may occur, that is adjacent terminals may be unintentionally connected by a solder bridge. A process which reduces this tendency is most desirable.
Flux is normally applied to areas to be soldered and the flux may contain volatiles or moisture which are desirably driven off before the terminals are soldered. The current move to volatile free fluxes makes this particularly important since water is now a common ingredient.
Solder balls are also produced in some processes and any reduction in their formation is desirable.
In accordance with the present invention a PC board (a printed circuit board) is delivered by a conveyer line to a solder station which is provided with pockets arranged to conform to the terminal arrangement, some times referred to as the xe2x80x9cfoot printxe2x80x9d of the printed circuit. Each pocket is arranged to be filled to overflowing with molten solder. An atmosphere of hot inert gas is provided to cover the surface of the solder at all times. To economize on the flow of inert gas a cover is provided in the form of a box with its lower open end immersed in the solder and its upper surface provided with apertures conforming to the xe2x80x9cfootprintxe2x80x9d so that pockets or terminals can enter the apertures and be surrounded with a flow of inert gas. In addition the terminals are exposed to the hot gas prior to soldering, preheating the area and driving off moisture and volatiles and minimizing production of solder balls The atmosphere of hot inert gas is continued after soldering, minimizing oxidation and bridging between terminals.
Also, to minimize bridging, the board is not raised vertically but is tilted as it is raised causing the solder to peel back while it is exposed to the hot inert atmosphere and thus maintained fluid.
A clearer understanding of my invention may be had from a consideration of the following description and drawings in which: